Directive scanning antenna system



July 1 1950 w. J. EALBERSHEIM 2514,61 7

DIRECTIVE SCANNING ANTENNA SYSTEM Filed April 13, 1946 FIG.

BEAM CROSS-SECTION\O FIG. .3

NEEDLE BEAM smuo I IN AL L DIRECTIONS FIG. 5

c. p. smsgw "I RANGE AZ/HUTH 2 Sheets-Sheet 1 FIG. 2

BEAM CROSS SECTION LONG/TUO/NAL SECTION FIG. 6

c. n. SCREEN *2 ELEVATION RANGE INVENTOR W J ALBERSHE/M A77 RNEY y 1950w. J. ALBERSHEIM 2,514,617

DIRECTIVE SCANNING ANTENNA SYSTEM Filed April 13, 1946 2 Sheets-Sheet 2FIG. 7

SCAN

CA 271005 RA) OSC/L LOSCOPE RANGE RANGE lNl/ENTOR W J ALBERSHE/M BY ATTORNEV Patente July it, 195

ll". ANTENNA SYSTEM Walter r. Albersheim, ilnteren, N. 3., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y a corporationof New York Application April 13, 1946, Serial No. states (oi. sis-1o) 3illaims.

dicular fan beams and to resolve without am-- biguity multiple targetslocated at equal ranges.

Another object of the invention is to rapidly and precisely determinethe location of targets by coupling together a rapid fan beam scanner.

with a. precise needle beam scanner.

Referring to the figures of the drawing:

Figs. 1 and 2 represent cross-sections of the beams shown in Figs. 3 and4 respectively:

Fig. 3 illustrates a needle beam;

Fig. 4 illustrates a fan beam;

Fig. 5 shows a cathode-ray screen for depicting range vs. azimuthcoordinates of targets derived by a radar;

Fig. 6 shows a similar cathode-ray screen depicting elevation vs. rangeof the said targets;

Fig. 7 shows a double ian beam antenna system; and

Fig. 8 shows a combined fan beam and needle beam antenna system.

A needle beam may be defined ideally as a. beam confined to a straightline. In practice however, a certain spread laterally is experienced,which may be of the order of 1.5 degrees or there abouts, as illustratedin Figs. 1 and 3.

A fan beam may be defined as being sharp in one plane and broad in theother, and having in general the configuration of a fan i. e., a lateralspread of degrees or more in one direction and 1.5 degrees in the other,as illustrated in Figs. 2 and 4.

In certain radar systems, such as ground operated anti-aircraft firecontrol, a. rapid and precise scan of an extended solid angle isrequired to search for and follow rapidly moving targets.

Since point-by-point scanning by means of a needl beam as in televisionwould be too slow, it has been suggested that radio fan beams be usedfor scanning the search area by single sweeps. To efiectivey determinethe location of a target, two crossed fan beams mutually perpendicularto each other are utilized. The sweep of one fan beamdetermines theazimuth of the target,-while the sweep of the perpendicular fan gle,lone target within the field of view is come pletely and unambiguouslydetermined by two correlated echo images, for example, spots A and D ontwo separate cathode-ray tubes (Figs. 5 and 6), one representing rangevs. azimuth, the other representing elevation vs. range.

However, when a flight of multiple airplanes appears in view, specifictarget identification becomes diificult and ambiguous. The cathode-rayscreens are then flooded with so many target presentations thatcorrelation between individual azimuths and corresponding elevations isrendered practically impossible.

The resulting uncertainty, in identification can be greatly reduced byselecting one of the possible targets on one of the screens showingrange and gating the range. By gating is meant the biasing of thereceiving amplifiers to extinction at all times, in a known manner,except for a short time interval corresponding to the twoway travel timeof an electromagnetic wave to and from a target within th chosen range.

Referring to Figs. 5 and 6, representing the coordinates appearingon theseparate cathoderay screens namely, azimuth vs. range, and range vs.elevation respectively, the faint dots shown therein represent themultiple targets whose apparance on the screens is suppressed by theaforementioned range gating. The two heavy dots shown on each screen,namely (A, B) and (C, D) represent two targets located at equal rangesfrom the radar equipment. It is obvious that a true correlation betweenazimuth and elevation for these two target echoes is indetermihate-fourcombinations AC, AD, BC, BD being possible-two representing the truetarget coordinates and the other two representing false or pseudotargets. Should the gunner select echo image A in Fig. 5 as a target, hewould be at a loss to determine whether to point his sights toward C orD on the elevation scale (Fig. 6).

With n targets at equal range, the ambiguity increases as n and theprobability of scoring a hit is reduced by a factor n. s

In accordance with one embodiment of the invention, the ambiguity whicharises with respect to multiple targets located at equal ranges, may befully resolved by slowly rotating one or both of the fan beam antennasaround an axis directed at a target. The true target may bedistinguished by the invariance of its position on the cathode-rayscreens with respect to the rotation, whilst the positions of the pseudotargets move or are displaced in accordance with the rotation.

Another embodiment of the invention contemplates determinate and rapidscanning, by combining the characteristics of fan beam scanning withneedle beam scanning, through a linking or coupling together of thecorresponding antennas.

Referring to Fig. 7, a pair of perpendicular fan beam antennas 2, 3 areshown, each comprising a rectangular wave guide feed horn and a pillboxshaped reflector with divergent flares 6 at the mouth thereof formatching the pill-box antenna to free space. The rectangular feed may bea bent pipe with a flared mouth (not shown) located at the focus of theparaboloidal-shaped pill-box, whereby a fan-shaped beam may be radiatedinto space. The pill-boxreflector has the shape of a D, and its detailsare more fully disclosed in the copending application of W. D. Lewis,Serial No. 574,334, filed January 24, 1945, which corresponds to theBritish Patent 606,927 accepted August 23, 1948, or in an articleentitled Microwave Radar Antennas by E. M. Purcell published inRadio-Electric Engineering, vol. 67, May 1946, pages 3-6.

The antennae 2, 3 shown in Fig. 7 are respectively connected toconventional transceiver equipment well known to the radar art andrepresented in said figure schematically by the rectangular blockdesignated Radar Circuit. This equipment may take various forms asexemplified for instance by U. S. Patent 2,475,707 issued July 12, 1949to P. A. Jeanne, by U. S. Patent 2,422,697

issued June 24, 1947 to L. A. Meacham, by U. S.

Patent 2,419,205 issued April 22, 1947 to C. B. H. Feldman, and by U. S.Patent 2,426,182 issued August 26, 1947 to 0. E. De Lange.

These patents illustrate and describe the association and operation ofthe various essential components of a radar circuit, such as, themagnetron, the pulser, the wave guide plumbing," the TR box, the rangingcircuit, the radio receivers and the cathode ray oscilloscopes.

the screen as illustrated in Figs. 5 and 8, an ambiguity in correlatingtheir true elevations and azimuths arise. To resolve this ambiguity, theoperator performs the final step of rotating the polar axis 6. If bothantennas are centered on the same target, the polar axis will bepointing directly at this target, and will continue to do so regardlessof polar rotation. In this case, one of the points C, D remainsstationary during the rotation of the polar axis, whereupon the polarrotation is stopped, the elevation of the antenna is locked in by anautomatic follower (not shown) and the gun is in proper firing position.

If, on the other hand, the antennas point at pseudo or false targets,rotation of the polar axis 6 has the effect of causing the images C, Dto be displaced along a circular arc. This displacement apprises theoperator of a false target correlation between an azimuth and elevationimage, whereupon he'will readjust his elevation until a target imageremains steadily centered and unaf- The two radars may operate on thesame frequency or on different frequencies, or if desired, one mayemploy a common transmitter with the antennae 2, 3 sharing its output ona time division or energy division basis.

The azimuth versus range indications are displayed on a cathode rayoscilloscope connected to antenna 2, while the elevation versus rangeindications are correspondingly displayed on the cathode rayoscilloscope co, ected to antenna 3 as shown in Fig. 7.

The pill-box antennas are rigidly connected by a rod 4, bent anddisposed so that the planar portions of said pill-boxes are mutuallyperpendicular. By means of this arrangement, a pair of crossedperpendicular fan beams are thereby radiated from the open mouths of thepill-boxes.

A solid angle in space, for example, at least 15 degrees square, may bescanned by the crossed fan beams, by rocking or oscillatingsthe feedhorn 2' horizontally and feed horn 3' vertically along a straight line.When each of these scanning fan beams strikes a target, an echo isreflected therefrom which produces a visible signal on a cathode-rayoscilloscope screen, as illustrated in Figs. 5 and 6.

The pair of antennas 2, 3 as a unit may be rotated or swung aroundthrough an azimuthal angle by rotating pedestal support I. When theazimuth of a target is found, it may be locked in by an automaticfollower (not shown). The elevation angle 0 is adjusted by rotating rod4 in its bearing at the top of the pedestal.

When multiple targets at equal range appear on fected by polar rotation,indicating correct coordinate association. Thereupon, he will lock inthe automatic elevation follower.

In accordance with another embodiment of the invention, it has beendetermined that rapid, pre cise and unambiguous coordinate determinationin'object location with radio beams may be obtained by rigidly couplingtogether a fan beam scanner and a needle beam scanner. Thus, in theembodiment illustrated in Fig. 8, the centering of the fan beam on thetarget for determination of one coordinate (azimuth) concomitantlyswings the rigidly coupled needle beam to the proper azimuth. The needlebeam is then swept vertically to determine the other coordinate, i. e.,the elevation.

Referring to Fig. 8, two antennas I and 8 are shown, namely, a fan beamradiator I of the "pill-box type aforementioned, and a needle beamradiator I of the paraboloidal type such as is disclosed in the UnitedStates Patent of A. C. Beck, 'No. 2,409,183 issued October 15, 1946. Thetwo antennas are rigidly coupled together by a rod 8, which constitutesan axis for the elevational adjustment of the antennas I, I. The pair ofantennas may be rotated as a unit about the azimuthal pedestal axis Hi.The feeds II, I! for the. antennas comprise rectangular pipes or horns.

The system shown in Fig. 8 operates in the following manner: 7

The rotational axes 9, III are set in the approximate direction of thetarget.

Feed horn II is rapidly oscillated sideways to produce a lateral sweepof the vertical fan beam radiated from the pill-box antenna 1. When thisbeam strikes a target, it is centered and locked-in by an automaticfollower (not shown). The azimuth position of the antenna assembly andgun are thereby fixed.

Then, feed horn I3 is rapidly rocked or oscillated up and down toproduce a vertical sweep of the needle beam radiated by antenna II, for

determining the elevational coordinate of the.

. in. The gun is now ready to fire.

Various forms of fan beam radiators may be asiasn utilized, such aseloated cylindrical aboloids, cylindrical lenses or elongated sectionsof paraboioids of revolution.

Various other forms of needle beam radiators antennas providing crossedfan beams for target whereby unambiguous resolution of multiple targetsat equal ranges may be provided.

2. In a radar system, a pair of directive radio antennas each having aplane of principal action, scanning means to sweep the plane of actionof each of said antennas about a respective sc axis, support means forsaid pair of antennas adapted for rotation of said pair jointly about afirst rotational axis and independent rotationof said pair jointly abouta second rotational ams perpendicular to the first, further supportmeans for one of said antennas adapted for independent rotationaladjustment of said one antenna about a third rotational amsperpendicular to the secend, said one antenna being supported with itsas each of said antennas about a respective scanning axis, support meansfor said pair of antennas adapted for rotation of said pair jointly 46about a first rotational axis and independent ro-,

tation of said pair jointl abo t a tional axis perpendicular to thefirst, f

rotaarmpport means for one of said antennas adapted for independentrotational adjustment of said one antenna about a third rotational axisperpendicular to the second. said one antenna being supported with itsscanning axis perpendicular to said third rotational axis, and the otherof said antennas being supported with its scanning axis perpendicular tosaid second rotational axis, transceiver means coupled to. both of saidantennas for supplying radio frequency waves thereto and receivingtherefrom echoes returned by distant reflecting objects, individualoscilloscopes for said antennas, circuit means responsive to the echoesreceived from one of said antennas for indicating on one of saidoscilloscopes the range and relative azimuth of the objects from whichsaid last-mentioned echoes are received, and circuit means responsive tothe echoes received from the other of saidan for indicating on the otherof said oscillosco the range and elevation of the objects from whichsaid last-mentioned echoes are received, whereby with said thirdrotational axis aligned with one of said objects the ambiguity of theindications in the presence of another object at the same range can beresolved by observing the eflect of said rotational adjustment on thesaid indications.

WALTERLAIB i i CES 9H The'following references are of record in the fileof thlspatent:

UNITED STATES PA I Number I Name Date 2,231,929 Lyman Feb. 18, 19412,256,787 Lazar Sept. 23, 1941 2,415,095 Varian et al. Feb. 4, 19472,417,248 Godet Mar. 11, 1947 2,421,028 King May 27, 1947 2,422,697Meacham June 24, 1947 2,28,829 Ferrell July 15, 1947 OTHERREFERENCES Thesea-26s Radar, Electronics, September was, pp. loo-10s.

